Display panel or portion thereof with a graphical user interface



FIG. 1 is a front view of a display panel or portion thereof with a graphical user interface, showing a first embodiment of our new design; and,

FIG. 2 is a front view of a display panel or portion thereof with a graphical user interface, showing a second embodiment thereof.

The broken line illustrating the display panel or portion thereof forms no part of the claimed design. The broken lines illustrate portions of the graphical user interface that form no part of the claimed design. 

CLAIM The ornamental design for a display panel or portion thereof with a graphical user interface, as shown and described. 